Known from the prior art, and in particular from document WO2005/090156, is a propulsion unit for an aircraft, comprising:                a fan comprising a fan case whereof the inner wall includes a coating whereof the upstream edge is set back in relation to the upstream edge of said case, and        an air intake assembly comprising an air intake structure comprising an air intake lip and an acoustic shroud extending between said air intake lip and the upstream edge of said coating.        
In this propulsion unit of the prior art, and traditionally, the acoustic shroud is made integral with the fan case by an annular flange, such a flange being connected on one hand to the fan case and on the other hand to the acoustic shroud by respective fastening means.
Such an arrangement requires sufficiently significant dimensioning of the acoustic shroud to have the necessary resistance with regard to stresses passing through the areas connecting said shroud with said flange.